The present disclosure relates to a method of manufacturing a power transmission belt, and a power transmission belt.
A power transmission belt for use in power transmission generally includes a tension member layer in which a cord is embedded and helically spun along a belt length direction, and a compressed rubber layer provided with ribs extending in the belt length direction or uniformly spaced cogs in the belt length direction.
The cord of the power transmission belt is ideally helically spun on the same plane with uniform cord spacing. The power transmission belt is wound around pulleys, and runs while being pulled on a substantially straight line between the pulleys. If the cord is arranged on the same plane, a predetermined tension is uniformly applied to positions of the cord. However, if the arrangement of the cord is disorganized in the belt thickness direction, the following problems occur. For example, suppose that some portions of the cord are deviated radially outwardly. In such a situation, if the belt is wound around the pulleys such that the inner circumference of the belt is in contact with the pulleys, the radially outwardly deviated portion is wound around the pulleys with a large radius of curvature. As a result, the radially outwardly deviated portion is excessively pulled. Also, if the belt is wound around the pulleys such that the outer circumference of the belt is in contact with the pulleys, the radially outwardly deviated portion is wound around the pulleys with a small radius of curvature. As a result, the belt comes loose.
Also, when the cord is embedded and a layer underlying the cord is formed into the shape of a truncated cone, portions of the cord are wounded around one side of the underlying layer with a larger radius of curvature than around the other side of the underlying layer. When the belt in such a condition is wound around the pulleys arranged in a layout, a very strong tension is applied to portions of the cord wound around the side of the underlying layer with a smaller radius of curvature, and portions of the cord wound around the side of the underlying layer with a larger radius of curvature are significantly loose.
As can be seen, if the arrangement of the cord in the belt width direction is disorganized, and the cord is not arranged on the same plane, the tension is not uniformly applied to each of the portions of the cord, resulting in bending of the belt. This causes the belt to snake and to slip off from the pulleys. Also, the portions of the cord to which a strong tension has been applied may be cut early. If the cord is cut, the belt disadvantageously fractures from the cut portions of the cord.
Furthermore, if the arrangement of the cord in the belt width direction is disorganized, and the cord spacing in the width direction is not uniform, the tension which has been applied to the cord is transferred to the pulleys through a rubber member, and this tension serves as a force pulling the pulleys. Thus, in a portion where the cord spacing is small, an excessive force is applied to the rubber member, resulting in early separation between the cord and rubber or an early crack in the rubber.
In order to avoid such an early fracture in the belt, it is recommended to wind the cord around a cylindrical mold with substantially uniform cord spacing. Use of a flat belt may relatively easily provide such an ideal configuration. However, unlike the flat belt, in the case of using, e.g., a V-belt and V-ribbed belt, it is difficult to allow the cord to have an ideal configuration.